This invention relates to a lead frame support plate and window clamp for wire bonding machines.
To ensure proper and accurate wire bonding, a lead frame needs to be held in place with respect to a wire bonding machine and FIG. 1 illustrates a conventional approach. FIG. 1 shows part of a wire bonding machine 100 comprising a window clamp 102 placed over a strip of lead frame 104 and a lead frame support plate 106 for supporting the strip of lead frame 104. The window clamp 102 includes two support sections 108 which are held by corresponding window clamp holders 110 for applying a clamping force to the window clamp 102.
FIG. 2 is an enlarged side perspective view of the part of the wire bonding machine 100 of FIG. 1 without showing the window clamp holders 110. The wire bonding machine further includes a heater block 112 for heating the lead frame support plate 106 and thus, the strip of lead frame 104 during the wire bonding process.
FIG. 3 is a perspective view of the lead frame support plate 106 of FIG. 2 which includes a series of elongate side bores 114 and a multiplicity of micro-holes 116 (normally more than 1000 micro-holes 116) across a major part of the lead frame support plate 106. The micro-holes 116 are in fluid communication with corresponding side bores 114 to create a network of air channels. When the side bores 114 are sealed up and a vacuum force is applied at the base of the lead frame support plate 106, a balanced suction force is created via the micro-holes 116 at the top surface of the lead frame support plate 106 to maintain the position of the strip of lead frame 104 during the wire bonding process. However, forming of the micro-holes 114 is an extremely time-consuming process.
Further, referring to the arrangement illustrated in FIG. 2, it has been found that with the lead frame support plate 106 and the strip of lead frames 104 heated to a high temperature (for example, 200° C.), the window clamp 102 is subjected to uneven heat distribution because the window clamp's lower surface which is in contact with the strip of lead frames 104 would have a higher temperature than the window clamp's upper surface since the upper surface is exposed. This uneven heat distribution together with the clamping force asserted by the window clamp holders 110 would cause the window clamp 102 to deform or warp. FIG. 4 shows an exemplary window clamp 300 which has deformed due to the uneven heat distribution. Such deformation would result in loose contact of the window clamp with leads of a lead frame resulting in floating leads or pads due to an insufficient clamping force therebetween. The bonding quality would thus be affected.
It is an object of the present invention to provide a lead frame support plate and window clamp which addresses at least one of the disadvantages of the prior art and/or to provide the public with a useful choice.